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Stuff You Should Know

The Mystery of the Sleepy Sickness

Published October 2, 2025
View Show Notes

About This Episode

The hosts explore encephalitis lethargica, also known as the sleepy sickness, a mysterious early 20th-century epidemic that caused profound sleep disturbances, movement disorders, psychiatric changes, and often death. They explain von Economo's classification of acute and chronic forms, the later emergence of post-encephalitic parkinsonism, and how Oliver Sacks's work with L-DOPA inspired the book and film 'Awakenings.' The episode reviews competing theories about the disease's cause and transmission, modern autoimmune hypotheses, and the haunting experience of patients who were conscious yet immobile for decades.

Topics Covered

Sleep Autoimmune disease Neurology Encephalitis lethargica Pandemics Infectious disease Parkinsonism Medical history Oliver Sacks Film adaptation

Disclaimer: We provide independent summaries of podcasts and are not affiliated with or endorsed in any way by any podcast or creator. All podcast names and content are the property of their respective owners. The views and opinions expressed within the podcasts belong solely to the original hosts and guests and do not reflect the views or positions of Summapod.

Quick Takeaways

  • Encephalitis lethargica was a devastating, poorly understood epidemic starting around 1916 that caused extreme sleepiness, movement disorders, psychiatric symptoms, and often death, then mysteriously disappeared within a decade.
  • Von Economo classified acute cases into three forms-somnolent ophthalmoplegic, hyperkinetic, and amniostatic akinetic-all involving different combinations of hypersomnolence, eye paralysis, mania, and statue-like immobility.
  • Many survivors later developed chronic post-encephalitic parkinsonism, living for years or decades frozen in bizarre postures yet often retaining significant awareness.
  • Oliver Sacks's use of L-DOPA in the 1960s briefly "awakened" many such patients, an experience dramatized in the film 'Awakenings,' but side effects often forced discontinuation and a return to immobility.
  • Evidence for EL's contagiousness was mixed, environmental toxins were ruled out, influenza (including Spanish flu) was ultimately excluded, and modern researchers now favor an autoimmune process triggered by infection.
  • Despite more than 9,000 papers written during the epidemic and later work, the exact cause, mode of transmission, and reason for EL's disappearance remain unknown.
  • Only about 80 EL-like cases have been reported in the last 75 years, making the condition extremely rare today and difficult to diagnose definitively.
  • Observations of paradoxical kinesia-patients suddenly moving in emergencies, to music, or while doing meaningful tasks-highlight how little is understood about the brain's ability to override pathological patterns.

Podcast Notes

Introduction and framing of the sleepy sickness episode

Hosts, producer, and episode type

Josh introduces himself, Chuck, and producer Jerry, noting this will be a "good old-fashioned" Stuff You Should Know medical mystery episode[1:25]
Chuck jokes that Jerry looks frozen at her keyboard and describes raising her hand above her head where it would stay until moved back down[1:43]
• Josh links Jerry's mock condition to chronic encephalitis lethargica, setting up the topic with humor

Naming and basic description of encephalitis lethargica

They decide to refer to the condition mainly as EL or encephalitis lethargica and note it was also called the sleepy sickness or sleeping sickness[2:15]
They clarify that there is another, unrelated modern sleeping sickness spread by the tsetse fly in Africa with some similar symptoms but a different cause[2:20]
EL's main outbreak began in Europe around 1916 with sudden loss of mobility, coma-like or sleep-like states, and many deaths within days[2:53]
By 1919, EL had reached epidemic proportions on at least four continents and killed hundreds of thousands of people[2:59]
EL is considered a medical mystery because its origin, cause, and disappearance are still unknown, though very rare modern cases are occasionally recognized by symptom pattern[3:07]
Patients were not lying peacefully like Sleeping Beauty; they could be frozen mid-gesture with eyes open and mouths agape, resembling statues rather than sleepers[3:41]
• Josh describes patients potentially sitting with a hand raised in the air and mouths open in a silent scream, remaining that way for decades after childhood onset

Origins and early clinical observations of EL

Dr. Constantin von Economo's role in identifying EL

In 1916, Dr. Constantin von Economo at the University of Vienna's psychiatric neurological clinic began seeing unusual neurological cases[4:52]
Patients were labeled with diagnoses like meningitis, multiple sclerosis, or delirium, but their symptoms did not match these conditions[5:09]
Von Economo first ruled out neurological toxins, infections, and known neurological disorders, concluding that doctors were dealing with something new[5:15]
French physician Dr. Rene Cruchet had described similar cases around the same time but interpreted them as behavioral disorders[5:41]
• Von Economo instead argued the condition was infectious and epidemic, leading to the alternative name "von Economo encephalitis" in recognition of his framing

Initial symptom progression in EL

Early in the illness, patients often appeared to have influenza, with fever and cough-like symptoms most listeners are familiar with[5:53]
After this flu-like phase, a wide array of neurological symptoms emerged, which varied greatly in severity and presentation among patients[6:55]
A key early symptom was hypersomnolence, meaning overwhelming sleepiness that could progress to coma-like or sleep-like states[6:55]
• Josh notes that EL-related "sleep" is not truly restful; patients are easily awakened and may remain semi-aware of surroundings even while seemingly asleep
• Despite awareness, these patients could not avoid falling asleep and sometimes could not actually fall fully asleep despite intense sleepiness
Another phenomenon was freezing mid-action, such as stopping halfway through eating and not moving again until triggered by something like music[8:04]
Chuck underscores that although called the sleeping sickness, EL's sleep-related symptoms are pathological and disturbing, not desirable rest[8:21]

Demographics and acute outcomes

About half of known EL cases occurred in people aged 10 to 30, indicating a broad but youth-tilted age range[8:36]
Many patients died within one to two weeks after onset of symptoms[8:42]
• One case describes a girl walking home from a concert who suddenly experienced paralysis, fell asleep within 30 minutes, and died less than two weeks later
Some survivors fully recovered physically but exhibited long-term psychiatric or personality changes after EL[9:08]
• A study found four reports of people who became kleptomaniacs following EL and then were otherwise considered cured of the infection

Acute encephalitis lethargica: subtypes and symptoms

Overview of acute EL classification

Acute EL refers to the initial illness with flu-like and then neurological signs, which von Economo divided into three clinical forms[10:35]
The three forms, from most to least common, are somnolent ophthalmoplegic, hyperkinetic, and amniostatic akinetic[10:35]

Somnolent ophthalmoplegic form

This most common form is also the deadliest, killing more than half of affected patients[10:55]
Patients experience overwhelming sleepiness combined with ocular paralysis where the eyes do not move, even when stimuli are presented[11:03]
Associated neuropsychiatric symptoms include delirium, confusion, catatonia, and stupor[11:20]
In extreme cases, EL-induced psychosis could lead to horrifying self-harm behaviors[11:34]
• Josh cites a 1930s case of a young girl who, during a psychotic episode attributed to EL, pulled out all her own teeth and gouged out both of her eyes
• He uses this to illustrate how EL damages the brain in specific regions, generating a wide range of horrific symptoms

Hyperkinetic form

The hyperkinetic form is less common than the somnolent type and is marked by manic behavior and increased movement[12:11]
Patients can display mania, involuntary vocalizations, and jerky, restless movements[12:20]
Following the manic phase, patients enter a hypomanic or fatigued state with pronounced weakness[12:22]
Additional symptoms include hallucinations and nerve pain in the limbs and face[12:27]
A curious feature is a reversed sleep pattern in which patients are awake at night and sleepy during the day[12:30]

Amniostatic akinetic form and waxy flexibility

The amniostatic akinetic form is the least common but aligns with the iconic image of EL sufferers as frozen statues[13:07]
Patients are unable to move (akinesis) and may be stuck mid-gesture, such as with one arm raised and mouth open[13:24]
Waxy flexibility describes how caregivers can position limbs or the body, and the patient will maintain that position until moved again[13:36]
• Josh notes that this means patients can be posed in almost any way, so caregivers must act kindly and respectfully
Despite their immobility, patients are often mentally present and aware of surroundings, similar in some respects to locked-in syndrome[14:44]
They clarify that EL patients are not in classic locked-in syndrome but share the core experience of being conscious with limited or no outward responsiveness[14:44]
It was only after later medical discoveries that doctors fully appreciated how much awareness these frozen patients retained[14:33]

Scale of the EL pandemic and outcomes

EL was a true pandemic, but precise case numbers are unknown due to diagnostic difficulty and underreporting[15:49]
Estimates of total cases range from 500,000 to more than 1,000,000, and some scholars believe up to half of all cases were never reported[16:03]
Roughly one-third of patients died, one-third survived and were relatively okay, and one-third survived but later developed chronic EL symptoms[16:09]

Chronic encephalitis lethargica and post-encephalitic parkinsonism

Transition from acute to chronic EL

Chronic EL describes long-term effects that appear after the initial, acute EL episode has resolved or seemingly resolved[19:03]
Patients may have thought they had recovered fully or with only minor behavior changes, then suddenly develop severe immobility years later[19:29]
• Josh likens it to a ton of bricks dropping on someone who has been living normally for a decade, suddenly rendering them immobile for life

Chronic symptom profile and behavioral changes

Chronic EL symptoms mirror earlier akinetic cases but persist for years or decades, including profound movement disorders and rigidity[19:55]
Patients can experience mood swings, feelings of euphoria, and sometimes increased libido as part of chronic EL[20:05]
Psychosis emerges in about 30% of chronic EL patients[20:11]
Investigators also documented "excessive silliness" and frequent use of puns as a striking and unusual symptom of chronic cases[20:19]

Post-encephalitic parkinsonism (PEP) and its distinction from Parkinson's disease

The statue-like immobility with waxy flexibility became known as post-encephalitic parkinsonism (PEP)[21:22]
Josh explains that Parkinsonism is a group of movement and neurologic symptoms, and while Parkinson's disease includes Parkinsonism, not all Parkinsonism is Parkinson's disease[21:04]
A key difference: Parkinson's disease typically progresses gradually and predictably, whereas PEP can appear suddenly in an otherwise functioning person[21:43]
• Josh illustrates this by saying someone might be eating an animal cracker when PEP suddenly freezes them mid-bite for the rest of their life
Many chronic EL patients ended up in institutions, effectively frozen for decades except for rare, brief episodes of movement[22:32]

Awakenings: Oliver Sacks, L-DOPA, and the EL patients

Connection between EL and the film 'Awakenings'

Chuck notes that readers who find the symptoms familiar may recall the film Awakenings, based on neurologist Oliver Sacks' book about EL patients[22:24]
In 1966, Sacks worked with around 80 chronic EL patients at Beth Abraham Hospital in the Bronx[22:35]
By that time, EL had essentially disappeared and was a little-known medical footnote, so many doctors in the 1960s were unfamiliar with it[22:47]
Sacks described his patients as motionless figures stuck in strange postures with no hint of motion, which directly inspired the film's portrayal[23:13]
Robert De Niro plays the patient Leonard Lowe, and Robin Williams plays the Sacks-like doctor; the film follows Sacks's nonfiction book fairly closely aside from name changes and some artistic license[24:18]

Development and effects of L-DOPA

Neurology researchers developed L-DOPA (levodopa) in the late 1960s as a dopamine substitute for Parkinson's disease[24:07]
Released in 1967, L-DOPA brought akinetic Parkinson's patients "back to life" by dramatically improving their movement[23:38]
In Awakenings, the narrative pivot is when the doctor secures L-DOPA and administers it to the seemingly unreachable Leonard Lowe[24:53]
Real EL patients on L-DOPA often "woke up": they became aware, spoke, focused their attention, and took part in activities like going on field trips or playing musical instruments[24:20]
This response paralleled Parkinson's patients but also underscored differences between PEP and Parkinson's in how long the benefits lasted and what side effects emerged[25:18]

Limitations, side effects, and partial recoveries

While many patients initially responded extremely well to L-DOPA, over time they developed severe side effects[25:18]
In some cases, side effects were so extreme that doctors had to discontinue L-DOPA treatment[25:43]
Consequently, some patients who had briefly regained motion, speech, and engagement returned to statue-like states despite being conscious[24:58]
One of Oliver Sacks's patients, called Rose in his writing and Lucy in the film, recounted being aware of world events during her immobile decades but feeling disconnected from them[25:18]
• She described knowing about Pearl Harbor and President Kennedy's assassination but said these events did not feel real to her
• She reported that although she knew she was 64 in 1964 living in a chronic hospital, she felt 21 and as if it were still 1926 when she first "came to a stop"
• Her L-DOPA side effects were too intense, forcing discontinuation and a return to near-static existence
Chuck notes that while the movie's ending is very sad, in reality some patients eventually stabilized and were able to live somewhat improved lives without being permanently statuesque[26:52]

Unresolved questions: causes and transmission of EL

Abrupt emergence, extensive study, and disappearance

EL emerged abruptly around 1915-1916, devastated populations for roughly a decade, and then vanished as suddenly as it had appeared[27:48]
Approximately 9,000 scientific papers were written during the epidemic in attempts to understand EL[28:13]
Despite this effort, scientists failed to answer major questions, including how people caught EL and why it disappeared[28:21]

Conflicting evidence on contagiousness

Some observations suggested EL was not highly contagious, as in a family of seven living together where only one member became ill[28:49]
Other cases showed apparent clustering, as at the Derby and Derbyshire Rescue and Training Home, where one girl's illness was followed by 12 of 21 residents getting sick within two weeks[28:55]
• About half of the infected residents died within 10 days, strongly indicating a real infectious process rather than mass hysteria
Researchers proposed possibilities such as natural immunity in some individuals or different EL strains with varying levels of contagion, but none were proven[29:17]

Ruling out environmental toxins and defining encephalitis

Encephalitis is defined as swelling of the brain and/or spinal cord and can be caused by many different triggers[29:55]
One category is toxic encephalitis, caused by environmental toxins, which investigators considered as a possible explanation for EL[30:35]
Because no consistent environmental exposure pattern was found among EL cases, toxic encephalitis as a unifying cause was largely ruled out[30:37]

Infectious encephalitis and the Spanish flu link that wasn't

Infectious encephalitis-secondary to viruses, bacteria, fungi, or parasites-is the most common form and can be caused by agents such as herpes, measles, West Nile, and influenza[32:04]
Given EL's temporal overlap with the 1918 Spanish flu pandemic and its initial flu-like symptoms, many early researchers suspected influenza as the cause[32:11]
Von Economo himself leaned toward an influenza-related explanation at the time[32:04]
Later molecular studies reconstructed the Spanish flu genome from preserved tissue and compared it with EL brain samples[33:18]
No Spanish flu RNA was found in tissue from known EL victims, strongly indicating EL was not caused by Spanish flu[33:10]

Streptococcal and herpes hypotheses, and the Matheson Commission

Some evidence suggested that EL cases were preceded by streptococcal infections in a subset of patients[32:43]
In 1931, von Economo vaccinated dogs with streptococcus, inducing EL-like symptoms, but the results were not definitive proof of causation in humans[32:18]
A wealthy American businessman named Matheson, who had EL, funded a research commission that studied the disease for 13 years[33:37]
The Matheson Commission released four reports but ultimately could not identify a clear cause, concluding only that herpes might be involved[34:11]
• The hosts joke about the anticlimactic outcome of years of funded research yielding merely a "maybe herpes" conclusion, underscoring the difficulty of pinning EL down

Modern perspectives on EL, paradoxical movement, and brain function

Research lull and renewed insights via Parkinson's studies

After early-20th-century investigations and mid-century efforts like the Matheson Commission, active EL research largely subsided for about three decades[40:37]
Interest in EL resurfaced indirectly through Parkinson's disease research, particularly with the development and deployment of L-DOPA[40:42]

Paradoxical kinesia and sensory triggers in EL patients

Clinicians observed that EL patients who seemed incapable of movement could suddenly move under certain conditions[40:59]
Oliver Sacks demonstrated this by tossing a ball at seemingly immobile patients and seeing some of them catch it reflexively without moving their eyes[41:10]
• In one instance dramatized in the movie, he misjudged and hit a patient who was actually fully mobile and she responded indignantly, adding humor to the demonstration
Another reported pattern was a statue-like patient suddenly rising from a wheelchair to help another patient who had fallen, then sitting back down and reverting to immobility[41:33]
This phenomenon, where patients switch between immobility and mobility depending on context, is known as paradoxical kinesia or kinesioparadoxical behavior[42:45]
Paradoxical kinesia is considered a hallmark of post-encephalitic parkinsonism and is not typical for Parkinson's disease, though some overlap may exist[43:06]
Other triggers that could temporarily override EL symptoms include music, human touch, and loud or obnoxious sounds like sirens[43:51]
Even after starting L-DOPA, some patients still relied on such external stimuli to better control tremors, rigidity, or abnormal movements[44:32]
• A former cobbler requested a cobbler's bench; while working, he could hold nails in his teeth and hammer tiny nails into shoe heels, showing coordinated, precise movements
• His ability to function while engaged in meaningful work contrasted sharply with his otherwise severe symptoms, suggesting task-related brain activation modulated his condition
These paradoxical behaviors hint that certain brain circuits can override pathological patterns in specific circumstances, though the underlying mechanisms remain unknown[45:30]

Rarity of modern EL-like cases

In the last 75 years, only about 80 case reports worldwide have been documented as having EL-like presentations[45:24]
These modern cases often exhibit hypersomnolence, ocular paralysis, and neuropsychiatric features similar to historical accounts[46:31]
Because symptoms vary and there is no definitive test, doctors are often uncertain whether these cases are true EL or just resemble it[46:31]

Current treatments and von Economo's recognition

There is still no cure for EL; L-DOPA remains a mainstay for treating tremors and rigidity when Parkinsonian features are present[47:17]
Electroconvulsive therapy (ECT) may be used in some EL-like cases to address severe psychiatric manifestations[47:28]
Von Economo was nominated three times for the Nobel Prize in psychiatric medicine for his work on EL but never received the award[47:28]

The leading autoimmune hypothesis

Although von Economo originally suspected a primary infection, modern thinking points to EL as an autoimmune disorder triggered by infection[48:12]
The hypothesis is that an infection-potentially streptococcal, herpes, influenza, or others-produces proteins resembling those in specific brain regions[47:47]
The immune system, trained to attack the pathogen, then mistakenly targets these similar brain proteins, causing autoimmune encephalitis[49:49]
Affected brain regions align with those controlling movement, sleep, and behavior, providing a plausible explanation for EL's distinctive symptom combination[49:47]
Despite the plausibility of this model, specific causative pathogens and precise mechanisms remain unproven, so EL continues to be partly mysterious[49:58]

Emotional and philosophical reflections on EL

Human impact and terror of the condition

The hosts stress how terrifying EL is, particularly the idea of being conscious yet unable to move or communicate for years or decades[50:56]
They highlight the special cruelty of patients who temporarily regained their lives with L-DOPA only to return to immobility when treatment became untenable[50:03]
They encourage listeners to remember that behind the "fascinating" medical mystery are real people who endured immense suffering[50:49]

Listener mail: radio 'fart cart' and audio cartridges

Clarifying what a 'cart' is in radio production

Listener Jamie Lynn writes about Buffalo radio announcer Iron Mike Benson, who used a "heinous anus fart cart" to play fart sound effects on air[51:47]
She had assumed "cart" meant a physical cart holding many tapes, but learned from the hosts' A-tracks episode that it refers to a tape cartridge[51:25]
Radio carts were looped tape cartridges with multiple tracks that let DJs quickly cue specific sounds, functioning as an analog precursor to digital soundboards[52:08]
Jamie Lynn notes that such seemingly useless knowledge only becomes useful when later connected to other information, and she praises the show for this[52:39]
She adds that Stuff You Should Know is the one podcast she and her sister Ashley have not grown tired of, and the hosts thank her and her family[52:43]

Lessons Learned

Actionable insights and wisdom you can apply to your business, career, and personal life.

1

Even with intense scientific effort, some medical mysteries remain unsolved for decades, reminding us that knowledge is provisional and humility is essential when dealing with complex systems like the brain.

Reflection Questions:

  • • Where in your own work or life are you assuming you have the full picture when, in reality, your information might be incomplete or outdated?
  • • How could you build more room for uncertainty and revision into your decision-making processes?
  • • What is one area this month where you could consciously revisit an old assumption and look for new evidence or perspectives?
2

People who appear unresponsive or severely impaired may still have rich inner lives, so treating them with dignity, patience, and engagement is both ethically necessary and potentially therapeutically meaningful.

Reflection Questions:

  • • How do you currently behave around people who communicate or move differently, and what might that signal about the respect you grant them?
  • • In what situations could you slow down and assume more awareness and personhood in others than their outward behavior suggests?
  • • What concrete change could you make this week-at home, work, or in public-to better include and engage someone who seems withdrawn or limited?
3

Targeted stimuli like music, touch, or meaningful work can sometimes unlock surprising capacities in people with severe limitations, showing the power of environment and context in shaping behavior.

Reflection Questions:

  • • What kinds of environments or activities bring out your best focus, mood, or performance, and what does that say about your own sensitivities?
  • • How might you redesign a space or routine for someone in your life (or on your team) to better align with the conditions under which they function well?
  • • What is one small environmental or sensory adjustment you could experiment with this week to improve your own concentration or well-being?
4

Long-term research and investment can still end in ambiguous answers, so leaders and funders must be prepared to value rigorous inquiry even when it doesn't produce neat solutions.

Reflection Questions:

  • • Where are you demanding quick, tidy answers in domains that may inherently require long, uncertain exploration?
  • • How could you better evaluate the quality of a process (how rigorously something is investigated) instead of only the clarity of outcomes?
  • • What is one project or area where you could explicitly commit to a longer time horizon and tolerate more uncertainty in pursuit of deeper understanding?
5

Stories and narratives-like the book and film 'Awakenings'-can make obscure scientific issues emotionally real, influencing how society understands and prioritizes complex problems.

Reflection Questions:

  • • What difficult or technical issue in your world might benefit from being communicated through a compelling story rather than just data or arguments?
  • • How could you use narrative-examples, case studies, personal anecdotes-to help others grasp the human impact of a complex topic you care about?
  • • What is one step you could take this month to either seek out a story that deepens your understanding of a hard problem, or to share such a story with others?

Episode Summary - Notes by Harper

The Mystery of the Sleepy Sickness
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